How wide is the soybean burndown window?


If you have weeds pop up prior to planting soybeans you can control them with a burndown herbicide application. But what happens when rain and wind conspire to prevent you from applying a burndown and you have to control weeds after planting?

That’s the situation many Ontario growers are facing in 2019 as the wet spring pushes into mid-May and herbicide application windows continues to shrink.

For soybeans, is applying a burndown after planting an option? How wide is the spray window? Do you risk crop injury? We have some answers to those questions.

In this episode of the Soybean School, published in 2017, Ontario Ministry of Agriculture, Food and Rural Affairs weed control specialist Mike Cowbrough takes us to the Elora Research Station where he set up an experiment to examine what happens when different burndown herbicides are applied after the label-recommended timing, which restricts application three days after soybean planting. (Story continues after the video.)

Cowbrough says growers should always follow recommended application timings and rates, but he believes there may be situations where spraying a little late may be worth the risk if growers need to control glyphosate-tolerant Canada fleabane or giant ragweed.

Cowbrough concludes that different herbicides pose different levels of risk when applied up to six or nine days after planting. Based on this trial, he says applying both metribuzin and saflufenacil up to six days after planting is a reasonable risk to take if you are rewarded with better control of troublesome glyphosate-resistant weeds that could be even more problematic the following year.

Based on his research, Cowbrough says these two products give you more “wiggle room.” In both cases, he saw no reduction in stand, no significant crop injury and no yield loss with either metribuzin or saflufenacil.

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